Chapter 18 Flashcards
What are the two components of the mitochondria?
1) the inner membrane space between the outer and the inner membranes
2) the matrix, which bounded by the inner membrane
Where does oxidative phosphorylation take place?
in the inner mitochondrial membrane
T/F The inner membrane is permeable to nearly all ions and polar molecules.
False
What is oxidative phosphorylation?
the electron-transfer potential of NADH or FADH2 is converted into the phosphoryl-transfer potential potential of ATP.
T/F
A strong reducing agent (such as NADH) is poised to donate electrons and have a negative reduction potential.
True
T/F
A strong oxidizing agent (such as O2) is ready to accept electrons and has a positive reduction potential.
True
What is driving force of the electron transport chain?
the electron transfer potential of NADH and FADH2 relative to that of O2
The released energy from the reduction of O2 with NADH generates a _________ that is used for the synthesis of ATP and the transport of metabolites across the mitochondrial membrane.
proton gradient
__________ within the transmembrane complexes leads to the transport of protons across the inner mitochondrial membrane.
Electron flow
__________ is special electron carrier that shuttles electrons from Complex I to Complex II.
Ubiquinone (Q)
Where do the electrons of NADH enter the ETC?
Complex I
How do electrons from NADH enter the ETC?
the initial step is the binding of NADH and the transfer of its electrons to FMN. Electrons are then transferred to series of Fe-S clusters and then passed on to Q
T/F
When accepting two electrons, Q takes up two protons from the matrix as it is reduced to QH2.
True
How do electrons from FADH2 enter the ETC?
electrons from FADH2 are transferred to Fe-S centers of Complex II and then to Q for entry into the ETC
(electrons can also be transferred through glycerol phosphate dehydrogenase)
What is the function of Q-cytochrome c oxidoreductase (Complex III)?
to catalyze the transfer of electrons from QH2 to oxidized cytochrome c, a water-soluble protein, and concomitantly pump protons out of the mitochondrial matrix (2H+ to the cytoplasmic side)
What is a cytochrome?
an electron-transferring protein that contains a heme group
T/F
The iron ion of a cytochrome alternates between a reduced ferrous (+2) state and an oxidized ferric (+3) state during electron transport.
True
How does Complex III accept electrons?
In addition to hemes, the enzyme contains an iron-sulfur protein with an 2Fe-2S center. This coordination stabilizes the center in its reduced form, raising its reduction potential so that it can readily accept electrons from QH2
How does the Q cycle work?
Two QH2 molecules bind to the complex consecutively, each giving up two electrons and two H+. These protons are released to the cytoplasmic side of the membrane. One electron flows to a molecule of oxidized cyto c converting it to the reduced form. The second passes through the two heme groups of cyto b to an oxidized Q and reduces it to a semiquinone radical anion.
T/F4
On the addition of the second electron, the Q radical takes up two H+ from the matrix side. The removal of these two protons from the matrix contributes to the formation of the proton gradient.
True
How many protons are released to cytoplasmic side and how many protons are removed from the mitochondrial matrix in the Q cycle??
4
What does cytochrome c oxidase (Complex IV) do?
catalyze the transfer of electrons from the reduced form of cytochrome c to molecular oxygen
How many electrons are funneled to O2 to completely reduce it to H2O?
4
T/F
The copper centers of Complex IV alternate between Cu+ and Cu2+ as they accept and donate electrons.
True
Where is the active center of Complex IV where O2 is completely reduced to H2O?
Heme a3 and CuB, which are directly adjacent
What is sequence of electron flow from cytochrome c and Complex IV?
CuA/CuA - a - a3 - CuB
Describe the reduction of O2 to H2O
electrons from cytochrome c flow down the pathway, one stopping at CuB and the other at a3
as O2 binds, it takes an electron from each of the nearby ions to form a O2(-2) bridge
two more molecules of cyto c bind and release e-; the two ion-oxygen groups are reduced to CuB-OH, Fe-OH
the addition of two more H+ ions allows the release of of two molecules of H2O and resets the enzyme
Where do the 4 protons come from in the reduction of O2 to H2O?
the matrix
What are ROS?
reactive oxygen species such as OH radical, which can lead to oxidative cell damage
How does the body combat ROS?
through scavenging enzymes, Superoxide dismutase and catalyze which perform their reactions near the diffusion limit
What is the chemiosmotic hypothesis?
electron transport and ATP synthesis are coupled by a proton gradient across the inner mitochondrial membrane
What is a proton-motive force?
energy rich unequal distribution of protons, which can be thought of as a chemical gradient and a charge gradient
Where is F0 subunit?
embedded in the inner mitochondrial membrane
What does the F1 subunit contain?
the catalytic activity of the synthase
What is important about the gamma subunit?
breaks down the symmetry of the alpha-beta hexamer; each of the beta subunits is distinct by virtue of its interaction with a different face of gamma
What are the names of the hydrophilic half channels of the a subunit in F0?
the cytoplasmic half channel
the matrix half channel
How do protons “move across” the membrane?
Protons bond to aspartate sidechains in the half channels
the aspartic acid residues then rotate until the proton is in a proton poor environment
the proton is then released
What is significant about proton movement in Complex V?
the movement of protons through the half-channels from the high proton concentration of the cytoplasm to the low proton concentration of the matrix powers the rotation of the c ring, this in turn drives the rotation of the gamma subunit (the formation of ATP)
How are electrons from cytoplasmic NADH transferred in the liver?
malate-aspartate shuttle
Describe the malate-aspartate shuttle (up to the exchange for glutamate).
electrons are transferred from NADH to oxaloacetate forming malate which traverses the IMM in exchange for alpha-ketoG
malate is then oxidized by NAD+ in the matrix to form NADH in a reaction catalyzed by an enzyme in the CAC
the new oxaloacetate molecule undergoes a transamination reaction to form Asp, which can be transported to the cytoplasmic side in exchange for glutamate
Describe the malate-aspartate shuttle (from the exchange of glutamate).
glutamate donates an amino group to oxaloacetate, forming aspartate and alph-ketoG
in the cytoplasm, aspartate is deaminated to form oxaloacetate and the cycle is restarted
